This section provides background information related to the present disclosure which is not necessarily prior art.
The primary function of a valve stem seal in an internal combustion engine, for example, is to allow adequate lubrication at the valve stem/valve guide interface while minimizing internal oil consumption. Valve stem seals of this general type are known in the prior art, as shown in U.S. Pat. Nos. 5,558,056; 4,947,811; 4,909,202; 3,554,562; and 3,554,180, for example. (In addition, a two-piece valve stem seal of this general type is shown in U.S. Pat. Nos. 6,901,902 and 5,775,284, which are assigned to the same assignee as the present application.)
A valve stem seal assembly generally includes a rigid shell structure and a seal body, with the assembly having a generally hollow interior adapted to receive a valve stem guide. Typically the shell structure supports the seal body, which surrounds the valve stem in order to essentially “meter” the provision of oil for lubricating the valve guide's inner diameter and the outer diameter of the valve stem. At the same time, however, the valve stem seal serves to minimize the amount of oil that can be drawn into the combustion chamber or pass to the engine's exhaust. If the rigid shell is not properly located in relation to the valve guide, the sealing element might not properly seat upon the valve stem thus causing non-uniform pressures at the valve stem and valve guide, undesirable wear patterns on the seal or valve stem and unpredictable lubrication of the valve stem and valve guide.
Some prior art valve stem seals have had histories of cracked flanges during vehicle operations due to valve train harmonics and the resulting internal stresses at the flange portion of the valve stem seal. Some of such prior art valve stem seals also have not had sufficiently flat flange portions, thus further increasing the likelihood of flange cracking. If the flange portion is not sufficiently flat, the valve stem seal is susceptible to fatigue loading by the valve spring as the valve opens and closes, flexing the flange.
The present disclosure provides a valve stem seal which will offer greater resistance to the cyclical forces exerted by the valve spring which causes the flange of a valve stem seal or valve stem seal assembly to crack.